I’m looking for good sources on student error in writing to share with a colleague. Joseph Williams on “The Phenomenology of Error” is an obvious choice, but I’d also like to share a piece that condenses Mina Shaugnessy’s extended point in Errors and Expectations about how the incidence of error goes up as students learn new concepts — in other words, how error itself can be an indication of learning. I remember reading a shorter piece (was it one of Bartholomae’s, maybe?) that made this argument, with some data to back it up, but don’t recall what it was. Help me out?